Field of the Invention
Embodiments described herein generally relate to choline hydroxide compositions, variants thereof, and methods of preparing such compositions. Specifically, embodiments described herein relate to stabilizers for such compositions and methods of stabilizing such compositions.
Description of the Related Art
Choline hydroxide (trimethylhydroxylamine), and variant quaternary trialkylalkanolamines thereof, are used in the agricultural chemical industry as neutralizing agents for herbicidal active ingredients such as 2,4-dicholorophenoxyacetic acid (2,4-D-acid), 3,6-dichloro-2-methoxybenzoic (dicamba) acid, and N-phosphonomethylglycine (glyphosate). Products such as 2,4-D choline, dicamba choline, and glyphosate choline provide convenient forms for handling and distributing the component herbicides. Choline hydroxide may also be neutralized with hydrochloric acid to make choline chloride, which is used as animal feed. Choline hydroxide is also used in some semiconductor applications as a caustic component of electroless plating solutions or as a photoresist stripping reagent.
Choline hydroxide is made by reacting aqueous trimethylamine with ethylene oxide at a maximum temperature of 45° C. Variants are made by similar reactions involving different amines and alkylene oxides. If not stabilized, choline hydroxide decomposes to its volatile components and their adducts over time. Trimethylamine is a strong colorant and carries a strong odor of fish oil, making it easily detectable in a choline hydroxide mixture. Acetaldehyde may be produced by decomposition of choline hydroxide, and may oxidize or polymerize over time to paraldehyde. These decomposition products of choline hydroxide and its variants impart color to insufficiently stabilized solutions.
Sodium borohydride and lithium aluminum hydride, and their alkali metal variants, have historically been used as stabilizers for choline hydroxide in applications for which the presence of alkali metals is tolerated. In other applications, hydroxylamine salts such as hydroxylamine acetate and hydroxylamine sulfate may be used at relatively high levels such as 0.2 wt % or more. Formaldehyde and paraformaldehyde have been shown to stabilize choline hydroxide for applications tolerant of organic solvents. Sodium bisulfate, sodium metabisulfite, sodium sulfite, sodium thiosulfate, ammonium bisulfite, and ammonium bisulfate provide reasonable stabilization at low concentration levels, but decline in activity after 4 weeks at 40° C. Amines such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), dimethylaminopropylamine (DMAPA), isopropylamine (IPA), aminoethoxyethylamine (AEEA), and trimethylamine (TMA) have been found to work to varying degrees at high concentrations. However, solutions stabilized with TMA at concentrations from 0.2 wt % to 5 wt % turn black after one week at 40° C. Thus, there is still a need for a method of stabilizing choline hydroxide and its variants for long periods of time using low stabilizer levels for agricultural applications.